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Author Topic: 3 phase rotary converter  (Read 1106 times)

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Offline Dana

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3 phase rotary converter
« on: March 16, 2009, 07:55:31 AM »
I just read Scsmiths thread and didn't want to hijack it.  :) I was at a local small machine shop last week and we got talking about phase converters. The owner showed me his converter. It was made by one of his family members. Here is what I found to be interesting. It is only 5 hp and can power the entire shop with all the machines running at the same time. :o

To demonstrate he started the converter by throwing a switch to it at the same time he had a momentary switch that had to be held only until the motor came up to speed. He then turned on a large lathe that had a 10 hp motor left that running turned on a 5 hp lathe and a bridgeport that he didn't give motor rating on. The bridgeport was switched from full forward to full reverse without a stop between. He said that can't be done with static type converters.

I ask what his electric bill is and was told its around $50.00 per month. He said the electric company had been out to look at his setup. They pulled the covers of the phase converter panels and couldn't figure out how its working. I am guessing that the motor has also been slightly reworked.

Has anyone else come across a converter that can run more hp that the actual motor? If so I would be interested in seeing the wiring schematic as I would like to build one. I don't know this guy well enough to ask to get a better look at how he is doing it.
Grass-fed beef farmer, part time sawyer

Offline jdtuttle

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Re: 3 phase rotary converter
« Reply #1 on: March 16, 2009, 08:07:59 AM »
Get to know him, then let us all know how he's doing it ;D
Jim
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Offline Fla._Deadheader

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Re: 3 phase rotary converter
« Reply #2 on: March 16, 2009, 09:31:20 AM »

 I would become friends with the family member.   ;) :) :)

  Might be a good idea to talk with the guy, and see what the cost would be to buy one from him.  You might even be able to furnish the motor, and save a few $$$ ???
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Offline Gary_C

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Re: 3 phase rotary converter
« Reply #3 on: March 16, 2009, 09:42:17 AM »
Nothing too revolutionary there. He is just using all the motors together to create the three phase. He needs to start them all and leave them running before he puts one to work.

As far as the around $50 per month, ask to see the bill and see how far around $50 it runs. Or maybe he is not running all that much. Ask for proof.   :)
Never take life seriously. Nobody gets out alive anyway.

Offline Dana

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Re: 3 phase rotary converter
« Reply #4 on: March 16, 2009, 10:09:20 AM »
Nothing too revolutionary there. He is just using all the motors together to create the three phase. He needs to start them all and leave them running before he puts one to work.

GaryC I may have been unclear in my explaination. He dosen't need to start all the machines to use one  or more machines. He started a few of the machines just to show how the 5 hp converter could run more a machine larger than 5hp and that it could run multiple machines at once. When I walked into his shop only one lathe was running.

Harold, I am going toask him if he can have his relative build me one if I can't find someone here that knows how it's done. I have a few old 3 phase motors around none are 5 hp or bigger though.
Grass-fed beef farmer, part time sawyer

Offline Fla._Deadheader

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Re: 3 phase rotary converter
« Reply #5 on: March 16, 2009, 10:25:07 AM »

 I have a diagram around here, somewheres ::) ::) ::) ::), that was sent to me by someone on the FF. I don't have any 3 phase stuff to run, so, I packed that diagram into my "Later on" projects folder, wherever that may be ???

  Seems to me you mostly need to use capacitors to balance out all 3 legs on the output, so the voltage is as equal as possible ???  A Google should turn up some good info, maybe  ::) ::) ;D ;D
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Offline Gary_C

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Re: 3 phase rotary converter
« Reply #6 on: March 16, 2009, 10:43:33 AM »
There is a lot of good info on making a converter right here on the forum. Try this one:

http://www.forestryforum.com/board/index.php/topic,22798.0.html
Never take life seriously. Nobody gets out alive anyway.

Offline logwalker

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Re: 3 phase rotary converter
« Reply #7 on: March 16, 2009, 12:54:58 PM »
It is not too hard to explain. You start the first motor, the converter. Holding the momentary switch activates a bank of capacitors to get it moving. Once it is up to speed you release the switch and some of the capacitors fall out of the circuit. Now the converter motor is spinning at rated rpm and is generating the third leg, the so called Wild leg of the 3 phase.

Each new motor that you start uses 2 legs from the 220 volt circuit and the Wild leg to run. Now the wild legs of both motors are in common with each other and each effectively reinforces the other one.

He was able to start a 10 hp motor from a running 5hp because it was starting with a light load. You can't do that with a heavily loaded motor on start up. Now he has a Wild leg that is stronger than it was on just the 5hp motor. Each new motor in turn builds on the whole.

The limiting factor is the size of the circuit feeding the the motors. Each motor could be on its own 2phase 220v breaker. To safely control a 3 phase motor you break any 2 legs feeding the motor. Most RPC (rotary phase converter) setups i have worked with use a single large breaker feeding the 3 phase circuit. That would limit the number of motors on the system.

If I am wrong on any of this feel free to correct me. Joe
Let's all be careful out there tomorrow. Lt40hd, 22' Kenworth Flatbed rollback dump, MM45B Mitsubishi trackhoe, Clark5000lb Forklift, Kubota L2850 tractor


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